Polytetrafluoroethylene is a unique compound commonly employed when one or more of the associated characteristics of chemical inertness, water repellency, and/or electrical insulating value are desired.
Polytetrafluoroethylene can be processed to form a highly porous breathable material which continues to retain the characteristics of chemical inertness, water repellency, and electrical insulating value. Briefly, such porous materials are generally produced by heating and expanding (stretching) a paste-formed body of the polytetrafluoroethylene.
Expanded porous polytetrafluoroethylene films may be used alone or laminated to an assortment of substrates to produce a variety of products including specifically, but not exclusively, sealing thread, breathable/water-repellant fabrics, air filters, liquid filters, vascular grafts (U.S. Pat. Nos. 3,953,566, 3,962,153, 4,208,745, 4,234,535, 4,321,711 4,332,035, 4,550,447, 4,647,416, 4,742,480, and 4,955,899), and numerous others.
Expanded porous polytetrafluoroethylene films have commanded wide acceptance since their introduction because is of their unique combination of properties. However, efforts continue in an attempt to improve upon these properties and thereby increase the potential uses of expanded porous films of polytetrafluoroethylene. One area of concentrated research has been with respect to efforts to increase the radiation resistance of the films, which are notoriously susceptible to degradation by radiation.
Efforts to improve upon the properties and/or uses of porous polytetrafluoroethylene materials by blending an additional component into the polytetrafluoroethylene prior to expansion have met with limited success. In fact, common wisdom in the art advises against incorporation of a matrix interactive component into the polytetrafluoroethylene prior to expansion, except in trace amounts, as a high degree of crystallinity is thought to be necessary to achieve proper expansion of polytetrafluoroethylene and the addition of a matrix interactive component tends to adversely affect the crystallinity.
A singular success in this area is described in U.S. Pat. No. 4,764,560, wherein incorporation of a silicone elastomer into polytetrafluoroethylene resin prior to expansion, followed by polymerization of the silicone elastomer, produces a porous silicone/polytetrafluoroethylene interpenetrating polymeric network having enhanced properties.
Because of the exceptional potential for further unique uses of polytetrafluoroethylene-containing materials, research continues in an effort to improve upon the properties and/or uses of the material.